In order to transport ocean freight containers filled with bulky and heavy goods, the goods should be conveyed or hoisted into containers and then fixed. Patent “U.S. Pat. No. 4,976,365 - - - Pallet and container integrated with pallet” discloses a kind of movable pallet with rollers at the bottom. In this patent, goods or small containers may be conveyed to and fixed on the pallet firstly; then, the pallet will be pushed into the ocean freight container; finally, the pallet can be fixed in the container. However, in actual use, locking structure of the patent is poor in reliability. While loading, each container is 20′ and even 40′ length, so the forklift has to be used for pushing at a long distance. While pushing, it's very hard to ensure that the pallet will be pushed stably in parallel along inner wall of the container, and the front corner of the pallet are liable to collide with wall of the container. Although a rubber pad is added to each front corner of the pallet and side wheels are set at both sides, while actual loading, the friction between rubber pad and side wall of the container is high, so it's hard to push. Transport environment is severe; the rubber pad is liable to be worn and fractured; steel structure of the pallet is hard; loading goods are very heavy; side wall of the container is generally made of thin corrugated steel plate (2 mm thick only), so edges and corners of the pallet are liable to crash and cut into side wall of the container and damage it. Besides, the principal axis of side wheels as referred to in the patent and the structure of the rolling bearing are weak and can't be impacted.
Patent “200380103526.2 - - - Mobile Pallet with Various Locking Means” discloses a kind of pallet for use with an ocean freight container, comprising: a chassis having a leading edge, a trailing edge opposite the leading edge and two opposite sides between the leading edge and the trailing edge; locomotion means for rolling chassis into, and out of, a freight container; a locking device is provided at two sides of, and located at, either the leading edge or the trailing edge of the pallet for immobilizing the chassis within the freight container with the locking device able to be engaged with a container wall, or another, adjacent pallet, to one side of the plurality of sides of the initial pallet for use with the freight container. The locking device if further able to engage a container wall, or the adjacent pallet, to the leading edge or the trailing edge of the initial pallet for preventing movement in mutually perpendicular directions in a horizontal plane. In this patent, various kinds of locking devices are set at leading corner, trailing corner and trailing center of the mobile pallet, so as to restrict the right and left clearance within the container by pivot structure of the leading corner and cylindrical spiral structure of the trailing corner and the leading and trailing clearance within the container by ratchet regulation structure of the trailing center. However, in actual use, these locking devices are complicated in structure and poor in reliability; the pivot structure of the leading corner is liable to be blocked and can't rotate flexibly; the spiral cylindrical structure of the trailing corner is cantilever beam structure and bears high shear force, so it often bends and breaks. If the spiral cylindrical structure bends, it can't rotate, leads to can't retreat from the slot; the pallet can't move; the goods can't be unloading; the spiral cylindrical structure must be cut off by force, so as to continue to work; however, if the spiral cylindrical structure is cut off, it will be unable to open the container; the whole pallet and goods may move freely and roll out of containers and result in an accident. The ratchet regulation structure of the trailing center has many components and is liable to be damaged, and the ratchet regulation structure can't be adjusted seamlessly due to its working principle. In conclusion, the above defects badly restrict wide application of the mobile pallet.